Acute, subacute and chronic sequelae of horses accidentally exposed to monensin-contaminated feed

Ultrastructural changes in cardiac and skeletal myoblasts following in vitro exposure to monensin, salinomycin, and lasalocid

Carboxylic ionophores are polyether antibiotics used in production animals as feed additives, with a wide range of benefits. However, ionophore toxicosis often occurs as a result of food mixing errors or extra-label use and primarily targets the cardiac and skeletal muscles of livestock. The ultrastructural changes induced by 48 hours of exposure to 0.1 μM monensin, salinomycin, and lasalocid in cardiac (H9c2) and skeletal (L6) myoblasts in vitro were investigated using transmission electron microscopy and scanning electron microscopy. Ionophore exposure resulted in condensed mitochondria, dilated Golgi apparatus, and cytoplasmic vacuolization which appeared as indentations on the myoblast surface. Ultrastructurally, it appears that both apoptotic and necrotic myoblasts were present after exposure to the ionophores. Apoptotic myoblasts contained condensed chromatin and apoptotic bodies budding from their surface. Necrotic myoblasts had disrupted plasma membranes and damaged cytoplasmic organelles. Of the three ionophores, monensin induced the most alterations in myoblasts of both cell lines.

Ionophores

Ionophores are a class of polyether antibiotics that are commonly used as anticoccidial agents and growth promotants in ruminant diets. Ionophores transport ions across lipid membranes and down concentration gradients, which results in mitochondrial destruction, reduced cellular energy production, and ultimately cell death. Cardiomyocytes are the primary target in equine patients when exposed to toxic concentrations and the clinical disease syndrome is related to myocardial damage. Animals can survive acute exposures but can have permanent heart damage that may result in acute death at future time points. Animals that survive a poisoning incident may live productive breeding lives, but physical performance can be greatly impacted. Animals with myocardial damage are at risk of sudden death and pose a risk to riders.

Accidental monensin poisoning in goats

Sodium monensin is the most frequently used ionophore as a growth promoter in ruminant diets. It has numerous benefits; however its toxic effects have also been observed in several animal species. Naturally occurring cases have not yet been reported in goats. This study describes an outbreak of accidental poisoning, characterizing its clinical, laboratory and pathological findings. Thirty-seven of 40 Anglo Nubian goat kids became intoxicated after receiving a diet that was erroneously supplemented with sodium monensin. They ingested an estimated toxic dose between 25 and 39 mg/kg BW. Clinical evolution was monitored (n = 27), followed by serum creatine kinase (CK) and aspartate aminotransferase (AST) activities measurements, and blood gas analysis. Postmortem examinations were performed between 1 and 8 days of evolution (n = 14). Clinical signs began 5 h after ingestion and included reticuloruminal hypomotility, lethargy, anorexia, tachycardia, cardiac arrhythmia, wet cough, pulmonary and tracheal crackles, and serous nasal discharge. The morbidity and lethality rates were 92.5 and 62.1%, respectively. CK and AST activities increased, reaching median values of 10,860 and 1596 U/L, respectively; the hyperchloremic metabolic acidosis was mild. The lesions were characterized by degeneration and necrosis of the cardiac and skeletal muscles, pulmonary congestion and edema, and passive liver congestion. The kids essentially developed cardiomyopathy with left and right congestive heart failures. Unlike in other ruminant species, skeletal muscle functional disability was infrequent. It can be concluded that monensin is toxic to goats and should be used with caution in their diet.

Monensin inhibits mast cell mediated airway contractions in human and guinea pig asthma models

Asthma is a common respiratory disease associated with airway hyperresponsiveness (AHR), airway inflammation and mast cell (MC) accumulation in the lung. Monensin, an ionophoric antibiotic, has been shown to induce apoptosis of human MCs. The aim of this study was to define the effect of monensin on MC responses, e.g., antigen induced bronchoconstriction, and on asthmatic features in models of allergic asthma. Tracheal segments from house dust mite (HDM) extract sensitized guinea pigs were isolated and exposed to monensin, followed by histological staining to quantify MCs. Both guinea pig tracheal and human bronchi were used for pharmacological studies in tissue bath systems to investigate the monensin effect on tissue viability and antigen induced bronchoconstriction. Further, an HDM-induced guinea pig asthma model was utilized to investigate the effect of monensin on AHR and airway inflammation. Monensin decreased MC number, caused MC death, and blocked the HDM or anti-IgE induced bronchoconstriction in guinea pig and human airways. In the guinea pig asthma model, HDM-induced AHR, airway inflammation and MC hyperplasia could be inhibited by repeated administration of monensin. This study indicates that monensin is an effective tool to reduce MC number and MCs are crucial for the development of asthma-like features.

Hepatoprotective and renoprotective effects of silymarin against salinomycin-induced toxicity in adult rabbits

Background and Aim: Salinomycin sodium, a licensed coccidiostat in rabbits, is used for fattening at a dose of 20–25 mg/kg. Salinomycin toxicity may arise from many risk factors (e.g., overdosage or use in non-target animal species). Silymarin extracted from milk thistle has antioxidant, anti-inflammatory, and antiviral properties. This study aimed to investigate the adverse impacts of oral administration of salinomycin for 28 consecutive days and how to reduce its risks and side effects by administering silymarin. Materials and Methods: Eighty-four male New Zealand White bucks (1.750–2.000 kg) were randomly divided into seven groups (12 each). Group one was the control. Groups two and three were administered salinomycin orally (doses of 20 and 40 mg/kg ration). Group four was administered salinomycin (20 mg/kg ration) and silymarin (6.5 mg/kg body weight [BW]). Group five received salinomycin (40 mg/kg ration) and silymarin (13 mg/kg BW). Groups six and seven were administered silymarin at doses of 6.5 and 13 mg/kg BW. Rabbits were euthanized and slaughtered on day 29 using the Halal method. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine, urea, total proteins, albumin, total cholesterol, and high- and low-density lipoprotein (HDL and LDL) were analyzed in serum. Glutathione (GSH), superoxide dismutase (SOD), catalase, and malondialdehyde (MDA) were estimated in the liver. A histopathological investigation was performed on the liver and kidney. Results: The MDA activity, AST, ALT, total protein, albumin, total cholesterol, triglyceride, LDL, urea, and creatinine values were significantly elevated in groups two and three. The GSH, catalase, SOD, and HDL were significantly lower in these groups than in the control group. There were moderate pathologic changes in the liver and kidney of the third group . However, the results of the fourth and fifth groups improved more than those of the second and third groups. The results of the sixth and seventh groups were nearly the same as those of the control group. Conclusion: Salinomycin toxicity was caused by oxidative damage because of reactive oxygen species formation. Silymarin (6.5 or 13 mg/kg BW) tends to prevent and treat accidental toxicity. However, the high dose of silymarin (13 mg/kg BW) had more renal and hepatoprotective capacities.

The In Vitro Cytotoxic Effects of Ionophore Exposure on Selected Cytoskeletal Proteins of C2C12 Myoblasts

Carboxylic ionophores, such as monensin, salinomycin and lasalocid, are polyether antibiotics used widely in production animals for the control of coccidiosis, as well as for the promotion of growth and feed efficiency. Although the benefits of using ionophores are undisputed, cases of ionophore toxicosis do occur, primarily targeting the cardiac and skeletal muscles of affected animals. The 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide (MTT) viability assay was used to determine the cytotoxicity of monensin, salinomycin and lasalocid on mouse skeletal myoblasts (C2C12). Immunocytochemistry and immunofluorescent techniques were, in turn, performed to investigate the effects of the ionophores on the microfilament, microtubule and intermediate filament, i.e., desmin and synemin networks of the myoblasts. Monensin was the most cytotoxic of the three ionophores, followed by salinomycin and finally lasalocid. Monensin and salinomycin exposure resulted in the aggregation of desmin around the nuclei of affected myoblasts. The synemin, microtubule and microfilament networks were less affected; however, vesicles throughout the myoblast’s cytoplasm produced gaps within the microtubule and, to a limited extent, the synemin and microfilament networks. In conclusion, ionophore exposure disrupted desmin filaments, which could contribute to the myofibrillar degeneration and necrosis seen in the skeletal muscles of animals suffering from ionophore toxicosis.

Residues of antibiotics in yeasts from ethanol production: a possible contamination route for feedingstuffs

Sugarcane yeast and brewer's yeast from ethanol production are widely used as ingredients of animal feed formulations in Brazil. To avoid the contamination of the must in ethanol production refineries, the use of antibiotics is one of the main preventive treatments. Thus, there is a risk of antibiotic residues carry over from yeast to animal feed. This unintentional addition of antibiotics can produce non-compliant feed products, due to regulatory aspects and their toxicity for animals. The results of an exploratory program to assess the occurrence of over 60 antibiotics and other pharmaceuticals in 27 sugarcane yeast and brewer's yeast samples were described. Monensin was present in seven samples with concentrations ranging from 0.47 to 263.5 mg kg^-1. Other antibiotics quantitated were virginiamycin (2.25 mg kg^-1) and amprolium (0.25 mg kg^-1). Monensin in sugarcane yeast may represent a risk for further feeds production, especially for those products intended for sensible species such as equines and rabbits, for which monensin has toxic effects.

Rhabdomyolysis and hepatotoxicity following accidental monensin ingestion: A report of two cases

BACKGROUND

Monensin is a commonly used veterinary antibiotic with a narrow safety range. Overdose of monensin can cause animal poisoning or even death. Monensin poisoning is rare in humans, and there is no effective detoxification protocol in clinical treatment.

OBJECTIVE

We report here two cases of monensin-induced rhabdomyolysis and hepatotoxicity by oral ingestion. The two patients were a couple and both were admitted to the hospital due to oral ingestion of monensin 5 days prior. Patient 1, with a past history of chronic bronchitis and hypertension, presented with severe rhabdomyolysis, hepatotoxicity, and hypoxemia. After treatment with fluid replacement and alkalinization of urine, his condition deteriorated the next day and irreversible cardiopulmonary arrest occurred. Patient 2 was diabetic and using oral hypoglycemic drugs and had obvious rhabdomyolysis from the fifth day of admission. After treatment with fluid replacement, urine alkalization, and continuous renal replacement therapy (CRRT), the patient recovered and was discharged 1 month later.

DISCUSSION

The ingestion of monensin can lead to life-threatening toxicity, with rhabdomyolysis and hepatotoxicity as the main manifestations. Comprehensive treatment including CRRT in the early stage of rhabdomyolysis may improve the condition and prognosis.